Dewey;
As a retired machinist I can certainly appreciate the workmanship you are putting into this. I will say from the pics it all looks absolutely First class. That combination shoe/through lump should give an extremely strong connection.
In the Bertuzzi, the outer plates are simply covers that open to expose the inboard-mounted sidelock mechanism.
I am not familiar with this gun, not following that inboard-mounted sidelock description. Is this somewhat akin to the old Lefever Arms Co guns. On those the lockworks were mounted to the frame with cover plates resembling a bar action sidelock. These guns though have traditionally been called box locks as the locks are not mounted to the plates.
